In prior art, magnetic field coupling type power transmission systems and electric field coupling type power transmission systems have been developed as wireless power transmission systems.
The magnetic field coupling type power transmission system includes a power transmitter device and a power receiver device, each of which includes a coil. In the magnetic field coupling type power transmission system, electric power is transmitted from the power transmitter device to the power receiver device by forming magnetic field coupling between the power transmitter side coil and the power receiver side coil.
The electric field coupling type power transmission system also includes a power transmitter device and a power receiver device, each of which includes a coupling electrode. In the electric field coupling type power transmission system, electric power is transmitted from the power transmitter device to the power receiver device by forming electric field coupling between the power transmitter side coupling electrode and the power receiver side coupling electrode, namely, by forming a capacitor including the power transmitter side coupling electrode and the power receiver side coupling electrode to transmit a high-frequency high-voltage signal through the capacitor.
The electric field coupling type power transmission system has the advantage that electric power may be transmitted from the power transmitter device to the power receiver device even when a relative spatial relationship between the power transmitter side coupling electrode and the power receiver side coupling electrode does not accurately satisfy a specific condition, compared to the case with the magnetic field coupling type where a relative spatial relationship between the power transmitter side coil and the power receiver side coil needs to be satisfied accurately.
An example of the electric field coupling type power transmission system described above is described in Patent Document 1, and includes a configuration of FIG. 15 as a basic configuration.
FIG. 15 is a diagram illustrating the basic configuration of a typical electric field coupling type power transmission system identical to the power transmission system described in Patent Document 1. The typical electric field coupling type power transmission system includes a power transmitter device 10 and a power receiver device 20. The power transmitter device 10 includes a high-frequency high-voltage generator circuit 11, a power transmitter side active electrode 12, and a power transmitter side passive electrode 13. The high-frequency high-voltage generator circuit 11 is connected to the power transmitter side active electrode 12 and the power transmitter side passive electrode 13.
The power receiver device 20 includes a high-frequency high-voltage load circuit 21, a power receiver side active electrode 22, and a power receiver side passive electrode 23.
When transmitting electric power from the power transmitter device 10, the power receiver device 20 is arranged on the transmitter device 10 in such a way that the power receiver side active electrode 22 overlaps with the power transmitter side active electrode 12 with a predetermined gap 4 in between them so as to have an overlapping area equal to or larger than a predetermined area. Furthermore, the receiver device 20 is arranged on the transmitter device 10 so as that part of the power receiver side passive electrode 23 also overlaps with the power transmitter side passive electrode 13 with the predetermined gap 4 in between them.
In the electric field coupling type power transmission system having the configuration of FIG. 15, power transmission efficiency is greatly affected by an overlapping area between the power transmitter side active electrode 12 and the power receiver side active electrode 22. The power transmission efficiency becomes higher as the overlapping area between the power transmitter side active electrode 12 and the power receiver side active electrode 22 becomes larger. The power transmission efficiency becomes lower as the overlapping area between the power transmitter side active electrode 12 and the power receiver side active electrode 22 becomes smaller. Thus, it is necessary to keep the overlapping area equal to or larger than a predetermined value all the time in order to achieve predetermined power transmission efficiency.
Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-531009
However, in the foregoing example in which, for example, the power receiver device 20 is placed on a top surface of the power transmitter device 10 without wiring the power receiver device 20 to the power transmitter device 10, the relative spatial relationship between the power transmitter device 10 and the power receiver device 20 is not always the same in a precise manner. The relative spatial relationship between the power transmitter side active electrode 12 and the power receiver side active electrode 22 may vary in some cases.
For example, when the power receiver device 20 formed of a rectangular housing is placed on the power transmitter device 10 such as a table, etc., to transmit electric power, a position of the power receiver device 20 on the power transmitter device 10 may vary two dimensionally in a plane perpendicular to a placing direction.
This two-dimensional variation in the relative spatial relationship sometimes may reduce the overlapping area between the power transmitter side active electrode 12 and the power receiver side active electrode 22, and reduce the power transmission efficiency.